Request for an ADAMHA RSA. This project will investigate the psychobiological factors that influence the preference for and consumption of carbohydrate-rich and fat-rich foods. There has been considerable concern that diets high in simple carbohydrates, and even more so high in fat, promote human disease and obesity. Laboratory research has documented that high-sugar and high-fat foods promote overeating, overweight, and obesity in animals. However, the psychobiological mechanisms responsible for these effects remain incompletely understood. Of particular importance are the determinants of food choice: why do animals (including humans) selecte sugar- and fat-rich foods when many food options are available? The orosensory properties (flavor) of high-sugar and high-fat foods are clearly attractive to animals. There is now good evidence that carbohydrate and fat appetites are also influenced by the postingestive actions of these nutrients. Until recently, these actions were considered to be exclusively inhibitory (satiating) in nature, but recent findings demonstrate that nutrients have positive (reinforcing) postingestive consequences that influence food choice and consumption by conditioning flavor preferences and acceptance. The specific aims of this project are to (1) compare the postingestive reinforcing and satiating effects of fat and carbohydrate. (2) Evaluate functional characteristics of nutrient reinforcement and satiety. (3) Determine the site(s) and route(s) of action of nutrient reinforcement and satiety. (4) Investigate the central neural mediation of nutrient reinforcement. To accomplish these goals, the project will use well-developed flavor preference conditioning procedures and nutrient infusion techniques.